I have created custom field in an existing model.

class Project_task_custom(models.Model):

    _inherit = "project.task"

    # inserting new field to project.task model

    customfield = fields.Integer("custom")

But How can I get existing field to calculate?

I want to get a field "__last_update" from related model such as account.analytic.line

And I want to compare them which one is latest one.

Then show the latest update time

I've made some code to archive it below

    @api.one

    @api.depends('timesheet_ids')

    def _get_has_timesheet(self):

        self.has_timesheet = bool(self.timesheet_ids)

    has_timesheet = fields.Boolean(compute="_get_has_timesheet", help="Technical field used for usability purposes")

Please help